The present invention relates generally to rotary grinders used for grinding things such as waste materials. More particularly, the present invention relates to rotary grinders having rotating arrangements of hammers.
Tub grinders for grinding waste material such as trees, brush, stumps, pallets, railroad ties, peat moss, paper, wet organic materials and the like are well known. An example of such prior art tub grinders is shown in commonly assigned U.S. Pat. No. 5,507,441 dated Apr. 16, 1996. Another example is shown in U.S. Pat. No. 5,419,502 dated May 30, 1995.
Tub grinders typically include a rotary grinding device such as a hammermill that is mounted on a frame for rotation about a horizontal axis. A rotating tub surrounds the grinding device. The tub rotates about a generally vertical axis. Debris is deposited in the rotating tub and the grinding device grinds the debris.
FIG. 1 illustrates one type of prior art hammermill 20 commonly used with conventional tub grinders. The hammermill 20 includes a plurality of hammers 22 secured to a plurality of rotor plates 24. The rotor plates 24 are rotatably driven about a generally horizontal axis of rotation 26. Cutters 25 (e.g., cutter blocks, cutter teeth, etc.) are mounted on the hammers 22 (e.g., with nuts 30 and bolts 28). The hammers 22 are secured between the rotor plates 24 by shafts or rods 31 aligned generally parallel to the horizontal axis of rotation 26. For example, each hammer defines two holes 32 and 34 each positioned to receive a different shaft 31 (only one shown). Shims 36 are mounted between the hammers 22 and the rotor plates 24. When the rotor plates 24 are rotated about the axis of rotation 26, the hammers 22 are carried by the rotor plates 24 in a generally circular path. Material desired to be ground is fed into the circular path such that the material is impacted and reduced in size by the cutters 25 of the hammers 22.
A conventional tub grinder also typically includes a sizing screen (not shown) that curves along a lower half of the hammermill. A grinding chamber is formed between the screen and the hammermill. The screen performs a sizing function and defines a plurality of openings having a predetermined size. In use, material desired to be ground is repeatedly impacted by the hammers 22 against the screen causing the material to be reduced in size. When the material is reduced to a size smaller than the predetermined size of the openings defined by the screen, the material moves radially through the screen. Upon passing through the screen, the reduced material commonly falls by gravity to a discharge system located beneath the hammermill 20.
Hammer wear is a significant concern relating to hammermills. For example, hammer wear results in loss of hammer integrity, out-of-balance conditions, reductions in grinding efficiency, and increases in maintenance and service costs. With a conventional hammermill, it is difficult to replace the hammers because the hammermill must be disassembled. Disassembling a hammermill can be particularly labor intensive and time consuming because the rods used to connect the hammers to the hammermill are quite heavy. There are typically several rods per hammermill and frequently two rods must be removed to replace a single hammer. Furthermore, rods can be corroded in place or deformed thereby making it even more time consuming and costly to disassemble a hammermill.
One aspect of the present invention relates to a rotary grinder having a cylindrical drum rotatable about its axis. The cylindrical drum has a cylindrical wall, a first end and a second end. The cylindrical wall defines a first receiving hole and a second receiving hole for receiving opposite ends of a through-member. The first end of the through-member extends to the outside of the cylindrical wall by passing through the first receiving hole such that the first end of the through-member comprises a first grinding portion (e.g., a hammer, cutter, blade, tooth, etc.) when the cylindrical drum is rotated. Likewise, the second end of the through-member extends to the outside of the cylindrical wall by passing through the second receiving hole such that the second end of the through-member comprises a second grinding portion (e.g., a hammer, cutter, blade, tooth, etc.) when the cylindrical drum is rotated. Thus, the through-member forms a duplex grinding member (e.g., a duplex hammer).
Another aspect of the present invention relates to a grinding device having a plurality of grinding members secured to a drum by a single retaining member that extends longitudinally through the drum.
In accordance with another aspect of the invention, a method for replacing a drum in a rotary grinder is presented. The rotary grinder includes a rotatable drum having a first end and a second end and a cylindrical surface. The rotary grinder also includes a plurality of hammers attached to the cylindrical surface and a first end cap attached to the first end of the drum and a second end cap attached to the second end of the drum. The method comprises the steps of removing the first end cap from the rotatable drum; removing the second end cap from the rotatable drum; replacing the rotatable drum with a second rotatable drum; attaching the first end cap to the first end of the second rotatable drum; and attaching the second end cap to the second end of the second rotatable drum.
A variety of advantages of the invention will be set forth in part in the description that follows, and in part will be apparent from the description, or may be learned by practicing the invention. It is to be understood that both the foregoing general description and the following detailed description are explanatory only and are not restrictive of the invention as claimed.